U.S. patent number 9,887,655 [Application Number 15/168,451] was granted by the patent office on 2018-02-06 for excitation current-limited power generator.
This patent grant is currently assigned to INFINEON TECHNOLOGIES AG, VALEO EQUIPEMENTS ELECTRIQUES MOTEUR. The grantee listed for this patent is Infineon Technologies AG, VALEO EQUIPEMENTS ELECTRIQUES MOTEUR. Invention is credited to Cedric Agneray, Frank Auer, Ludovic Doffe, Robert Hartmann, Christoph Seidl.
United States Patent |
9,887,655 |
Auer , et al. |
February 6, 2018 |
Excitation current-limited power generator
Abstract
An excitation current-limited power generator includes a digital
interface configured to be coupled to an engine control unit (ECU),
a regulator coupled configured to be coupled to an excitation
current input of an alternator, the excitation current controlling
current generated by the alternator, a frequency sensor configured
to measuring rotation speed of the alternator, and memory storing a
communicated limit received by the digital interface and a first
permanent limit, the regulator configured to limit the excitation
current to the lesser of the first permanent limit and the
communicated limit.
Inventors: |
Auer; Frank (Roehrmoos,
DE), Seidl; Christoph (Graz, AT), Hartmann;
Robert (Munich, DE), Doffe; Ludovic
(Beaurainville, FR), Agneray; Cedric (Estreelles,
FR) |
Applicant: |
Name |
City |
State |
Country |
Type |
Infineon Technologies AG
VALEO EQUIPEMENTS ELECTRIQUES MOTEUR |
Neubiberg
Creteil |
N/A
N/A |
DE
FR |
|
|
Assignee: |
INFINEON TECHNOLOGIES AG
(Neubiberg, DE)
VALEO EQUIPEMENTS ELECTRIQUES MOTEUR (Creteil,
FR)
|
Family
ID: |
60269356 |
Appl.
No.: |
15/168,451 |
Filed: |
May 31, 2016 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20170346431 A1 |
Nov 30, 2017 |
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H02P
9/006 (20130101); H02P 9/10 (20130101) |
Current International
Class: |
H02P
11/00 (20060101); H02P 9/00 (20060101); H02P
9/10 (20060101); H02H 7/06 (20060101); H02P
9/04 (20060101); F02N 11/06 (20060101) |
Field of
Search: |
;322/15,29 ;290/40R
;700/287 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Cuevas; Pedro J
Attorney, Agent or Firm: Slater Matsil, LLP
Claims
What is claimed:
1. A device comprising: a digital interface configured to be
coupled to an engine control unit (ECU); a regulator configured to
be coupled to an excitation current input of an alternator, the
excitation current controlling current generated by the alternator;
a frequency sensor configured to measure a rotation speed of the
alternator; and a memory configured to store a communicated limit
received by the digital interface and a first permanent limit, the
regulator configured to limit the excitation current to the lesser
of the first permanent limit and the communicated limit.
2. The device of claim 1, wherein the regulator is further
configured to periodically update the communicated limit with a
value received from the ECU.
3. The device of claim 2, wherein the value received from the ECU
is selected to limit the current generated by the alternator.
4. The device of claim 2, wherein the value received from the ECU
is selected to limit counter-torque induced in the alternator.
5. The device of claim 1, wherein the memory is further configured
to store a second permanent limit, and a rotation threshold
associated with the second permanent limit, wherein the regulator
is further configured to limit the excitation current to the lesser
of the second permanent limit and the communicated limit when the
rotation speed of the alternator is greater than the rotation
threshold.
6. The device of claim 5, wherein the first permanent limit is
greater than the second permanent limit.
7. The device of claim 5, wherein the first permanent limit is less
than the second permanent limit.
8. The device of claim 1, wherein the regulator is further
configured to limit the excitation current to the first permanent
limit in response to the digital interface losing connection with
the ECU.
9. The device of claim 1, further comprising the alternator.
10. The device of claim 9, wherein the alternator comprises a
rotating coil in stator coils.
11. A method comprising: receiving a communicated limit for an
excitation current in an alternator over a digital interface;
determining a permanent limit for the excitation current in the
alternator; limiting the excitation current to the communicated
limit in response to the communicated limit being less than the
permanent limit; and limiting the excitation current to the
permanent limit in response to the communicated limit being greater
than the permanent limit.
12. The method of claim 11, wherein determining the permanent limit
comprises: determining a rotation speed of the alternator; and
selecting a permanent limit from one or more permanent limits, the
one or more permanent limits each corresponding to a lower and
upper rotation speed threshold, the rotation speed of the
alternator being between the lower and upper rotation speed
threshold of the selected permanent limit.
13. The method of claim 12, wherein the one or more permanent
limits comprise a first permanent limit and a second permanent
limit, the upper rotation speed threshold of the first permanent
limit being less than the upper rotation speed threshold of the
second permanent limit.
14. The method of claim 13, wherein the first permanent limit is
greater than the second permanent limit.
15. The method of claim 13, wherein the first permanent limit is
less than the second permanent limit.
16. The method of claim 11, further comprising: receiving an
updated permanent limit over the digital interface; and storing the
updated permanent limit in memory.
17. A system comprising: an engine control unit (ECU); a digital
interface coupled to the engine control unit; an alternator coupled
to the digital interface, the alternator comprising: a memory
configured to store a communicated limit received from the digital
interface and a first permanent limit; an excitation current input;
and a regulator coupled to the excitation current input, the
regulator configured to control current output from the alternator
by varying the excitation current, the regulator configured to
limit the excitation current to the lesser of the first permanent
limit and the communicated limit.
18. The system of claim 17, wherein the alternator further
comprises a rotation sensor coupled to an output of the alternator,
the rotation sensor configured to measure a rotation speed of the
alternator.
19. The system of claim 18, wherein the memory is further
configured to store a second permanent limit, the first permanent
limit associated with a first rotation threshold and the second
permanent limit associated with a second rotation threshold, the
alternator configured to limit the excitation current to the first
permanent limit when the rotation speed of the alternator is less
than the first rotation threshold, the alternator configured to
limit the excitation current to the second permanent limit when the
rotation speed of the alternator is less than the second rotation
threshold.
20. The system of claim 17, wherein the alternator is configured to
update the first permanent limit stored in the memory with an
updated permanent limit received from the ECU over the digital
interface.
Description
TECHNICAL FIELD
The present invention relates generally to power generation, and in
particular embodiments, to techniques and mechanisms for an
excitation current-limited power generator.
BACKGROUND
Power generators typically include a rotating coil in stator coils.
The output current of stator coils may be controlled by changing an
excitation current flowing through the rotating coil. Some types of
power generators, such as alternators, are typically used in
applications that include combustion engines, e.g., passenger
automobiles, such that the power generator may be connected to the
powertrain of the combustion engine.
Power generators can experience degraded performance under harsh
environmental conditions, e.g., cold temperatures and lower
rotation speeds. Quick speed cycles of an engine, e.g.,
accelerating and decelerating, may result in a combustion engine
periodically operating at lower engine speeds. Further, research
efforts for passenger automobiles have increasingly focused on
lowering engine speeds in an effort to improve fuel efficiency.
Problems associated with operating power generators at lower engine
speeds have thus been exacerbated. The performance of power
generators in modern fuel-efficient automobiles may be further
worsened in colder climates.
Worsened performance of a power generator may result in the
generator exceeding the maximum rated output of the generator, or
may cause the generator to experience counter-torque from the
combustion engine. Such degraded performance can damage the power
generator over time.
SUMMARY OF THE INVENTION
Technical advantages are generally achieved by embodiments of this
disclosure, which describe techniques and mechanisms for an
excitation current-limited power generator.
In accordance with some embodiments, a device is provided. The
device includes a digital interface configured to be coupled to an
engine control unit (ECU), a regulator coupled configured to be
coupled to an excitation current input of an alternator, the
excitation current controlling current generated by the alternator,
a frequency sensor configured to measuring rotation speed of the
alternator, and memory storing a communicated limit received by the
digital interface and a first permanent limit, the regulator
configured to limit the excitation current to the lesser of the
first permanent limit and the communicated limit.
In some embodiments, the regulator is further configured to
periodically update the first communicated limit with a value
received from the ECU. In some embodiments, the value received from
the ECU is selected to limit the current generated by the
alternator. In some embodiments, the value received from the ECU is
selected to limit counter-torque induced in the alternator. In some
embodiments, the memory further stores a second permanent limit,
and a rotation threshold associated with the second permanent
limit, wherein the regulator is further configured to limit the
excitation current to the lesser of the second permanent limit and
the communicated limit when the rotation speed of the alternator is
greater than the rotation threshold. In some embodiments, the first
permanent limit is greater than the second permanent limit. In some
embodiments, the first permanent limit is less than the second
permanent limit. In some embodiments, the regulator is further
configured to limit the excitation current to the first permanent
limit in response to the digital interface losing connection with
the ECU. In some embodiments, the device further includes the
alternator. In some embodiments, the alternator comprises a
rotating coil in stator coils.
In accordance with some embodiments, a method is provided. The
method includes receiving a communicated limit for excitation
current in an alternator over a digital interface, determining a
permanent limit for the excitation current in the alternator,
limiting the excitation current to the communicated limit in
response to the communicated limit being less than the permanent
limit, and limiting the excitation current to the permanent limit
in response to the communicated limit being greater than the
permanent limit.
In some embodiments, determining the permanent limit comprises
determining a rotation speed of the alternator, and selecting a
permanent limit from one or more permanent limits, the one or more
permanent limits each corresponding to a lower and upper rotation
speed threshold, the rotation speed of the alternator being between
the lower and upper rotation speed threshold of the selected
permanent limit. In some embodiments, the one or more permanent
limits comprise a first permanent limit and a second permanent
limit, the upper rotation speed threshold of the first permanent
limit being less than the upper rotation speed threshold of the
second permanent limit. In some embodiments, the first permanent
limit is greater than the second permanent limit. In some
embodiments, the first permanent limit is less than the second
permanent limit. In some embodiments, the method further includes
receiving an updated permanent limit over the digital interface,
and storing the updated permanent limit in memory.
In accordance with some embodiments, a system is provided. The
system includes an engine control unit (ECU), a digital interface
coupled to the engine control unit, an alternator coupled to the
digital interface, the alternator comprising memory configured to
store a communicated limit received from the digital interface and
a first permanent limit, an excitation current input, and a
regulator coupled to the excitation current input, the regulator
configured to control current output from the alternator by varying
the excitation current, the regulator configured to limit the
excitation current to the lesser of the first permanent limit and
the communicated limit.
In some embodiments, the alternator further comprises a rotation
sensor coupled to an output of the alternator, the rotation sensor
measuring rotation speed of the alternator. In some embodiments,
the memory is further configured to store a second permanent limit,
the first permanent limit associated with a first rotation
threshold and the second permanent limit associated with a second
rotation threshold, the alternator configured to limit the
excitation current to the first permanent limit when the rotation
speed of the alternator is less than the first rotation threshold,
the alternator configured to limit the excitation current to the
second permanent limit when the rotation speed of the alternator is
less than the second rotation threshold. In some embodiments, the
alternator is configured to update the first permanent limit stored
in the memory with an updated permanent limit received from the ECU
over the digital interface.
BRIEF DESCRIPTION OF THE DRAWINGS
For a more complete understanding of the present invention, and the
advantages thereof, reference is now made to the following
descriptions taken in conjunction with the accompanying drawing, in
which:
FIG. 1 illustrates an automotive system;
FIGS. 2A and 2B illustrate example current and torque output
curves;
FIG. 3 illustrates a detailed view of a power controller;
FIG. 4 illustrates excitation current curves;
FIG. 5 illustrates an alternator over-current protection
method;
FIG. 6 illustrates output current curves; and
FIGS. 7A and 7B illustrate permanent limits for protecting an
alternator.
Corresponding numerals and symbols in the different figures
generally refer to corresponding parts unless otherwise indicated.
The figures are drawn to clearly illustrate the relevant aspects of
the embodiments and are not necessarily drawn to scale.
DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS
The making and using of embodiments of this disclosure are
discussed in detail below. It should be appreciated, however, that
the concepts disclosed herein can be embodied in a wide variety of
specific contexts, and that the specific embodiments discussed
herein are merely illustrative and do not serve to limit the scope
of the claims. Further, it should be understood that various
changes, substitutions and alterations can be made herein without
departing from the spirit and scope of this disclosure as defined
by the appended claims.
Disclosed herein are techniques and mechanisms for an excitation
current-limited power generator. Various embodiments include
self-protection mechanisms in a power generator limiting the
excitation current applied to the rotating coil of the power
generator. The excitation current may be limited based on a
measured rotation speed of the power generator. Excitation current
limitation thresholds may be selected to limit maximum current
output, measured in amperes (A), and/or counter-torque, measured in
newton-meters (N-m). Various self-protection mechanisms may be
applied independently of an engine control unit (ECU), which may
also monitor and control the excitation current or power supply
voltage level of the rotating coil.
Various embodiments may achieve advantages. Limiting current output
of the power generator may allow the generator to operate in
harsher environmental conditions, such as cold climates, without
exceeding maximum output of the generator. Ensuring the generator
does not exceed maximum output may avoid damaging the generator or
devices powered by the generator, such as passenger vehicle loads.
Limiting torque production of the power generator may allow the
generator to operate at lower speeds, such as low engine speed of a
passenger automobile, without damaging the generator or producing
undesirable side effects, such as humming, in the engine of the
automobile. Efficiency, reliability, comfort, and lifespan of
fuel-efficient vehicles may thus be improved.
FIG. 1 illustrates an automotive system 100 that may be used in an
automobile or other passenger vehicle such as a car or truck. The
automotive system 100 includes vehicle loads 102, a battery 104, an
alternator 106, and an ECU 108. While the present discussion is
presented in the context of passenger automobiles, it should be
appreciated that embodiments described herein may be applied to any
power generator with moving magnets.
The vehicle loads 102 include devices necessary to operate the
automotive system 100. Examples of vehicle loads 102 may include
the ignition, spark plugs, climate control, and entertainment
systems in the automotive system 100. The battery 104 provides an
initial charge to the vehicle loads 102 during ignition of the
automotive system 100. The battery 104 may, for example, be a 12
volt battery. Additionally, the battery 104 acts as an electrical
buffer for the output of the alternator 106.
The alternator 106 includes a rotating coil 110, stator coils 112,
rectifier diodes 114, and a power controller 116. The rotating coil
110 is located inside the stator coils 112, and includes a rotating
magnetic field (not illustrated). Rotating the magnetic field
created by the rotating coil 110 in the stator coils 112 generates
electrical current in outputs of the stator coils 112. There may be
three of the stator coils 112, such that the generated power is
three-phase alternating current (AC) power. The rectifier diodes
114 rectify the generated three-phase AC power to produce direct
current (DC) power. The DC power is delivered to power the vehicle
loads 102 and charge the battery 104.
The power controller 116 includes a voltage level input 118, a
rotation speed input 120, an excitation current output 122, and a
digital input/output (I/O) 124. The power controller 116 is coupled
to various components of the alternator 106 so that it may control
the amount of current generated by the alternator 106. Control of
the current output may be achieved by varying the excitation
current of the rotating coil 110. The power controller 116 may be,
e.g., an application-specific integrated circuit (ASIC) or a state
machine.
The voltage level input 118 is coupled to the rectifier diodes 114
so that the power controller 116 may measure DC power output by the
alternator 106. The voltage level input 118 may allow the power
controller 116 to determine whether the output of the alternator
106 has been exceeded. Such a protection mechanism may allow the
power controller 116 to reduce production by reducing the
excitation current of the rotating coil 110.
The rotation speed input 120 is coupled to one of the stator coils
112. As discussed above, there may be multiple stator coils 112,
such that the stator coils 112 generate three-phase AC power.
Coupling the rotation speed input 120 to one of the stator coils
112 allows the power controller 116 to measure the frequency of one
of the three-phase AC outputs. The frequency output from each of
the stator coils 112 corresponds to the rotation speed of the
alternator 106. Accordingly, by measuring the frequency of one of
the signals from the stator coils 112, the power controller 116 may
determine the rotation speed (in RPM) of the alternator 106.
The excitation current output 122 is coupled to the rotating coil
110. As discussed above, the output current of the alternator 106
may controlled by varying the excitation current of the rotating
coil 110. Accordingly, the power controller 116 may control the
output current of the alternator 106 through the excitation current
output 122. The power controller 116 may limit the excitation
current of the rotating coil 110 in response to communication from
the ECU 108 (discussed below) or in response to a self-protection
feature (also discussed below).
The digital I/O 124 allows the alternator 106 to communicate with
other devices in the automotive system 100, such as the ECU 108.
The digital I/O 124 may be capable of bi-directional digital
communication. Examples of such a communication system may include
a local interconnect network (LIN). Communication over the digital
I/O 124 may be performed in time-fixed schedule slots, such as
every 100 milliseconds (ms). The digital I/O 124 may be shared with
other devices in the automotive system 100, such that the power
controller 116 may only communicate with the ECU 108 during a
portion of the schedule slots. Accordingly, communication with the
ECU 108 may have a low throughput and a high latency.
The ECU 108 is coupled to the alternator 106 and other devices (not
pictured) in the automotive system 100 so that it may control and
monitor parameters of the devices. The ECU 108 communicates with
the alternator 106 through the digital I/O 124. Because the ECU 108
is capable of measuring many parameters in the automotive system
100, the ECU 108 may have access to more information than the power
controller 116, and in some situations may be able to more
accurately control output current or counter-torque produced by the
alternator 106. In some embodiments, the ECU 108 may control
production of the alternator 106 by communicating an excitation
current limit to the power controller 116.
In order to control the output of the alternator 106, the ECU 108
should be capable of supporting such functionality. As discussed
above, the digital I/O 124 between the alternator 106 and the ECU
108 may be slow, such that the ECU may not be capable of responding
to sudden changes conditions such as speed. Accordingly, brief
peaks of current output and/or counter-torque may occur in the
alternator 106 before the ECU 108 communicates a new excitation
current limit to the power controller 116. Further, the digital I/O
124 may fail, resulting in a temporary or permanent loss of
communication with the alternator 106. During these periods of lost
communication, damage may occur to the alternator 106. Over its
lifetime, these brief peaks of current and/or counter-torque may
wear on the alternator 106, reducing its lifecycle. Further, such
peaks may also harm the on-board power supply network of the
automotive system 100, such as the vehicle loads 102 and/or the
battery 104.
FIGS. 2A and 2B illustrate example current and torque output
curves, respectively, for an alternator at different excitation
currents. As can be seen in FIG. 2A, the maximum rated current
output of the alternator is about 315 [A], as illustrated by the
dashed line in FIG. 2A. Each of the output current curves of the
alternator increases with RPM and eventually converges on a final
output current. For example, at the lowest excitation current, the
output current gradually increases until it is outputting about 75
[A] at about 8000 RPM. Conversely, at the highest excitation
current, the output current sharply increases until it is
outputting about 350 [A] at about 8000 RPM. In some embodiments,
the alternator may operate at a higher excitation current when
driven at a lower RPM in order to quickly achieve sufficient
current output. In some embodiments, the alternator may operate at
a lower excitation current when driven at a higher RPM in order to
avoid excessive current output.
As can be seen in FIG. 2B, the maximum rated torque output of the
alternator is about 20 [N-m], as illustrated by the dashed line in
FIG. 2B. Each of the output torque curves of the alternator has a
peak at lower RPM, the amplitude of which is proportional to the
excitation current. For example, at the lowest excitation current,
the output torque peaks at about 2 [N-m] at about 3000 RPM.
Conversely, at the highest excitation current, the output torque
peaks at about 27 [N-m] at about 3000 RPM. In some embodiments, the
alternator may operate at a lower excitation current when driven at
a lower RPM in order to avoid torque peaks that may damage the
alternator. In some embodiments, the alternator may operate at a
higher excitation current when driven at a higher RPM, as there is
a decreased risk of torque peaks at a higher RPM.
FIGS. 2A and 2B illustrate a trade-off between current and torque
peaks, which may occur at higher excitation currents, and achieving
sufficient current output, which is difficult to achieve at lower
excitation currents. These peaks may occur over a relatively short
time periods, such that the ECU 108 may not respond to the peaks in
a timely manner. Accordingly, in some embodiments, the power
controller 116 may perform self-protection of the alternator 106
independent of the ECU 108 to avoid current and/or torque peaks
that may cause damage.
FIG. 3 illustrates a detailed view of the power controller 116. The
power controller 116 includes a bus 302, a communications
controller 304, a battery sensor 306, a frequency sensor 308, a
regulator 310, memory 312, and a master logic unit 314. Devices in
the power controller 116 may or may not be connected to the bus
302.
While they are shown as functional blocks, it should be appreciated
that the battery sensor 306, the frequency sensor 308, and the
regulator 310 may include other components to interface the power
controller 116 with components in the alternator 106. For example,
these devices may include transducers, analog-to-digital
converters, digital-to-analog converters, registers, amplification
circuitry, supporting circuitry, and the like.
The communications controller 304 is coupled to the digital I/O
124, and interfaces the alternator 106 with external devices, such
as the ECU 108. As discussed above, the digital I/O 124 may be a
bi-directional digital interface, such as LIN. As such, the
communications controller 304 may be, e.g., a LIN controller.
The battery sensor 306 is coupled to the voltage level input 118,
such that the power controller 116 may measure the output voltage
level of the battery 104 and the DC power output from the
alternator 106. The battery sensor 306 may, for example, be an
analog-to-digital converter. In some embodiments, the
analog-to-digital converter may be a 10-bit ADC.
The frequency sensor 308 is coupled to the rotation speed input
120, such that the power controller 116 may measure the frequency
of the output AC signal from one of the stator coils 112. The
frequency sensor 308 may, for example, comprise a linear
oscillator, such as a resistor-capacitor oscillator, which is used
to detect the frequency of the AC waves. The rotation speed of the
alternator 106 may thus be determined according to the measured
frequency and the quantity of phases rectified by the rectifier
diodes 114. By relating frequency of the AC signal to engine
rotation speed, the power controller 116 can determine rotation
speed of the alternator 106, independently of any engine speed
parameters that may be communicated via the communications
controller 304.
The regulator 310 is coupled to the excitation current output 122,
such that the power controller 116 may vary the excitation current
of the rotating coil 110. By varying the excitation current, the
regulator 310 may thus regulate and control and output current of
the alternator 106. The regulator 310 may, for example, be a
voltage regulator.
The memory 312 may be volatile memory, such as random access memory
(RAM), or non-volatile memory (NVRAM), such as EEPROM. In some
embodiments, the memory 312 includes both RAM and NVRAM. The NVRAM
may be implemented using fuses, electronic fuses (e-fuses), or
one-time programmable (OTP) memory. The memory 312 is used to store
limitation parameters (sometimes referred to as "limits"). Limits
are maximum excitation current values that the regulator 310 should
observe when varying the excitation current supplied to the
rotating coil 110. One or more limits may be included with the
memory 312, and the limit applied may be determined according to
different states of the alternator 106.
In some embodiments, a first type of current limit (sometimes
referred to as a "communicated limit") may be communicated to the
power controller 116 over the communications controller 304 and
stored in the memory 312. A communicated limit may be considered
immediately when determining the current supplied to the rotating
coil 110. A communicated limit may be stored in RAM or NVRAM
portions of the memory 312.
In some embodiments, a second type of current limit (sometimes
referred to as a "permanent limit") may be considered when
determining the current supplied to the rotating coil 110. The
permanent limit is stored in NVRAM portions of the memory 312, such
that it may be persisted in the power controller 116 after a loss
of power or a loss of communication with the ECU 108. Accordingly,
the power controller 116 may be capable of reading the permanent
limit from NVRAM and limiting excitation current to the permanent
limit during periods of lost or missing communication. For example,
excitation current may be limited during vehicle ignition, before
the ECU 108 has sent a communicated limit to the power controller
116. A permanent limit may be pre-programmed in the NVRAM. In some
embodiments, a permanent limit may be communicated to the power
controller 116 over the communications controller 304 from time to
time, and the permanent limit may be stored in NVRAM. It should be
appreciated that multiple permanent limits and/or communicated
limits may be stored in the memory 312.
In some embodiments, each of the permanent limits stored in the
memory 312 may be associated with an engine rotation speed
threshold, measured in RPM. The regulator 310 may select different
permanent limits to apply to the excitation current according to
the rotation speed determined by the frequency sensor 308. For
example, a first permanent limit may be associated with a first
rotation speed threshold, and a second permanent limit may be
associated with a second rotation speed threshold higher than the
first rotation speed threshold. The regulator 310 may apply the
first permanent limit when the measured rotation speed is less than
the first rotation speed threshold, and then may apply the second
permanent limit when the measured rotation speed is less than the
second rotation speed threshold. A hysteresis may be included with
each different rotation speed threshold applied.
In some embodiments, the regulator 310 may consider both a
permanent limit and a communicated limit when limiting excitation
current. The regulator 310 may prefer the lower of the permanent
limit and the communicated limit, such that the permanent limit is
not exceeded. In other words, if the communicated limit is lower
than a permanent limit that is currently applied, then the
regulator 310 may permit the excitation current to be lowered to
the communicated limit. However, if the communicated limit is
greater than the permanent limit, then the regulator 310 may not
permit the excitation current to be increased past the permanent
limit. The ECU 108 may thus apply a lower communicated limit, which
may allow the ECU 108 to perform torque management for the
alternator 106. However, the ECU 108 may not override the
alternator 106 with a higher permanent limit. Such a protection
mechanism may protect the alternator 106 and allow faster
protection reaction times when output current is quickly increased.
In some embodiments, the output of the alternator 106 may be
switched on or off if the voltage level measured by the battery
sensor 306 is less than the limit that the regulator 310 is
applying.
The master logic unit 314 is the main processing pipeline for the
power controller 116. It includes function units and/or circuitry
for performing start-up sequences, controlling the regulator 310
and the communications controller 304, and optimizing, testing, and
debugging the power controller 116. The master logic unit 314 may
also include functionality for interacting with the battery sensor
306 and the frequency sensor 308. The master logic unit 314 may
select a permanent limit from the memory 312 based on the measured
speed, and may determine whether to apply the permanent or
communicated limit to the regulator 310.
FIG. 4 illustrates the excitation current necessary to achieve an
ideal output current for an alternator at various engine speeds. An
ideal output current may be an output current that approaches the
peak output current. As illustrated by the solid line, at lower
speeds the alternator will not exceed peak output current even at
maximum excitation current, as lower engine speeds may not generate
enough power to exceed the peak output. However, as engine speed
increases, the permanent limit for the excitation current is
lowered in order to prevent the alternator from exceeding peak
output.
In some embodiments, the memory may include a permanent limit for
the engine speed corresponding to each data point forming the solid
line. The power controller may thus include sufficient permanent
limits for the excitation current so that the alternator does not
exceed peak output current at any engine speed. For example,
assuming an alternator has output characteristics similar to the
response illustrated in FIG. 4, the alternator memory would include
six permanent limits (ranging from about 6 [A] to about 4 [A]) at
respective rotation speed threshold (ranging from about 0 RPM to
about 6500 RPM) to ensure the alternator does not exceed peak
current output.
In some embodiments, the memory may include a relatively fewer
quantity of permanent limits. As such, the power controller may
limit the excitation current so that the alternator does not exceed
peak output current at most engine speeds. For example, the dashed
line in FIG. 4 illustrates an embodiment where only two permanent
limits (PLIM.sub.1 and PLIM.sub.2) are included in the memory. As a
result, when only two permanent limits are used, the alternator may
exceed or fall below peak current output for some engine speeds (a
small band between approximately 2500 RPM and 3500 RPM), but will
generally operate at or near an ideal output. More or less
permanent limits could be used, such that the alternator's response
characteristics are a closer or further approximation of the ideal
output.
FIG. 5 illustrates an alternator over-current protection method
500. The alternator over-current protection method 500 may be
indicative of operations occurring in the power controller 116 when
applying a permanent or communicated limit to the excitation
current produced by the regulator 310.
The alternator over-current protection method 500 begins by
evaluating a communicated limit (step 502). The communicated limit
may be received from an ECU. The communicated limit may be
periodically updated by the ECU. Next, a permanent limit is
evaluated (step 504). Evaluation of the permanent limit may include
selecting a permanent limit according to a measured rotation speed
of the alternator. Next, if the permanent limit exceeds the
communicated limit (step 506), the permanent limit is used to limit
excitation current (step 508). However, if the permanent limit does
not exceed the communicated limit (step 506), the communicated
limit is used to limit excitation current (step 510). Once either
the permanent or communicated limit is chosen, the value is then
passed to the regulator (step 512). The regulator may then choose
an excitation current for the rotating coils that does not exceed
the chosen limit.
FIG. 6 illustrates output current curves when one of several
permanent output limits are applied to the alternator. As shown, a
first permanent limit PLIM.sub.1 is applied for speeds less than an
engine speed threshold s.sub.12. A second permanent limit
(PLIM.sub.2) is applied for speeds greater than the engine speed
threshold s.sub.12. Accordingly, the output current approaches the
target maximum current output when the first (higher) permanent
limit is applied. Before the output current exceeds the maximum
current output, the second (lower) permanent limit is applied such
that the output current is reduced. Accordingly, the output current
of the alternator may not exceed the maximum current output,
avoiding damage to the alternator.
FIGS. 7A and 7B illustrate permanent limits for protecting an
alternator from excessive current output and excessive
counter-torque, respectively. FIG. 7A illustrates the application
of two permanent limits, where a lower permanent limit is applied
at higher engine speeds. Accordingly, FIG. 7A illustrates
excitation currents for a power controller operating in an
over-current protection mode.
FIG. 7B illustrates the application of two permanent limits, where
a higher permanent limit is applied at higher engine speeds.
Accordingly, FIG. 7B illustrates excitation currents for a power
controller operating in an over-torque protection mode. As
illustrated by the dotted lines, a hysteresis may be applied in
both current-limiting and torque-limiting operating modes.
Although the description has been described in detail, it should be
understood that various changes, substitutions and alterations can
be made without departing from the spirit and scope of this
disclosure as defined by the appended claims. Moreover, the scope
of the disclosure is not intended to be limited to the particular
embodiments described herein, as one of ordinary skill in the art
will readily appreciate from this disclosure that processes,
machines, manufacture, compositions of matter, means, methods, or
steps, presently existing or later to be developed, may perform
substantially the same function or achieve substantially the same
result as the corresponding embodiments described herein.
Accordingly, the appended claims are intended to include within
their scope such processes, machines, manufacture, compositions of
matter, means, methods, or steps.
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